The present invention pertains to magnetic couplings, and more particularly, it pertains to magnetic couplings comprised of annular arrays of angularly spaced permanent magnets sequentially polarized in opposite directions.
Magnetic couplings are devices utilizing magnetic fields to transmit torque between a driving member and a driven member without any physical contact between the members. Thus, they have been widely used on seal-less pumps, for example, wherein volatile, flammable, corrosive, abrasive, or foul-smelling liquids are being pumped and it is difficult or undesirable to use conventional seals to seal the drive mechanism from the driving impeller within the liquid. Magnetic couplings have also found wide use in pumps or rotary positioning devices that are designed to operate in a vacuum wherein the provision of seals about a mechanical force-transmitting coupling would obviously create problems.
Magnetic couplings typically include two annular assemblies or arrays of permanent magnets having south-pole and north-pole faces being spaced angularly about each of the arrays. The arrays can be arranged in a face-to-face relationship in an axial direction, i.e., with the arrays having a common axis of rotation and with the individual pole faces of the opposed arrays facing each other in a direction parallel to the axis of rotation, or, they can be arranged concentrically with the individual pole faces of the opposed arrays facing each other in a radial direction to the common axis of rotation of the arrays. One of such arrays is adapted to be connected to a motor or other driving means while the other array is adapted to be connected to a pump impeller or other member to be driven. When the arrays are at rest, i.e., when there is no load upon the coupling, the opposed north and south pole faces of the opposed arrays align with each other due to the attractive force therebetween and the repulsive forces of the adjacent pole faces. When the rotary drive force is applied to the one array, the other array is caused to rotate in synchronism therewith due to the attractive and repulsive forces mentioned. As a load is applied to the driven member, the arrays will continue to rotate synchronously although the pole faces on the driven array will trail the pole faces on the drive array by a small rotary angle. When an excessive load is applied exceeding the maximum torque that can be generated by the coupling, the arrays de-couple and the drive array will rotate by itself. Under such a condition, the drive must be stopped and restarted before the arrays can again be coupled and rotated in synchronism.
In conventional prior art magnetic couplings the adjacent north-pole and south-pole magnets of each permanent magnet array are spaced apart by air gaps or by non-magnetically conductive material, and the transfer of magnetic flux between the adjacent magnets within each array is provided by a separate magnetically conductive member physically connecting each of the north-pole and south-pole magnets at a location spaced from the gap. Examples of such prior art magnetic couplings, for example, are shown in U.S. Pat. No. 4,896,754 to Carlson et al.
In recent years various designs of motors and generators have been suggested and built utilizing a Halbach array of permanent magnets wherein the array is comprised of separately magnetized segments with spaced north-pole and south-pole segments and separately magnetized segments interposed between the north-pole and south-pole segments and magnetized in a direction transversely of the adjacent north-pole and south-pole segments. Examples of such motors and generators are shown in U.S. Pat. Nos. 5,631,618 to Trumper et al; 5,705,902 to Mettitt et al; 6,104,108 to Hazelton et al; 6,111,332 to Post; 6,169,352 to Hull; 6,188,147 to Hazelton et al; and 6,208,045 to Hazelton et al.